Add debug items to View menu

[nsakaimbo]

Description

This PR adds the following debug/developer items to the View menu:

• Reload
• Force Reload (ignore cache)
• Toggle Developer Tools

Enabling these items is triggered by the setting the environment variable WP_DESKTOP_DEBUG.

To Test/Use

Start the application in the terminal using the command WP_DESKTOP_DEBUG=1 open path/to/WordPress.com.app and verify the debug menu items appear in the View menu.

[matticbot]

Test live: https://calypso.live/?branch=desktop/debug-menu

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[codebykat]

I see that debug-menu.js predates this PR, but fwiw there's a defined Electron role for Dev Tools (toggleDevTools).

https://www.electronjs.org/docs/api/menu-item

We're not using it on the Simplenote side because I had to remove the shortcut due to a conflict.

Approving as the code looks good anyhow (I did not build the app)

[nsakaimbo]

there's a defined Electron role for Dev Tools (toggleDevTools)

Huh - TIL. I went ahead and amended the debug menu to use the default roles provided by Electron (0b55329). Tested and confirmed they appear to work as expected (e.g. Chrome DevTools are opened against the currently active window, without having to code this up manually). Also force reload is pretty handy (which ignores the existing cache).